This invention relates in general to metal cutting and more particularly to a machine for slitting metal sheet.
Much of the steel produced by mills is in the form of coiled steel sheet, but rarely does the sheet correspond in width to the multitude of products that are stamped or otherwise formed from it. Accordingly the steel sheet is usually slit longitudinally to sizes suitable for the particular products. Indeed, special slitting machines are made for this purpose.
The typical slitting machine has circular blades or knives arranged in pairs on two powered arbors, there being one knife of each pair on one of the arbors and the second knife of the pair on the other arbor. Actually each knife is nothing more than a hardened steel disk, perhaps about 10 inches in diameter and about 1/4 to 2 inches thick. It has flat end faces and a cylindrical peripheral face which intersects the end faces at relatively sharp cutting or shearing edges. The disks of each pair are positioned on their respective arbors, often with a slight overlap. Overlap or not, the knives of each pair are positioned close enough to each other to enable them to cut or shear the metal sheet as it passes between those knives. In other words, the metal sheet passes between the two knives of a pair--and indeed is drawn between them--the disk-like knives shear the sheet along the opposite cutting edges, thus producing a clean longitudinal cut in the sheet. Not only are the disk-like knives arranged in pairs, but the pairs of knives are also usually organized into left and right hand configurations to prevent the longitudinal segments of the slit sheet from acquiring a twist or spiral upon emerging from the slitting machine. Thus, each arbor usually carries at least two and often more knives.
The knives, while being fixed firmly on their respective arbors during the operation of the machine, nevertheless may be removed for sharpening or may be repositioned so that the width of the segments slit may be varied. Setting the knives on the arbors of a slitting machine however is a tedious and time-consuming procedure, requiring a high degree of skill, for the knives must be located with considerable precision, not only to acquire the proper width for the cut, but to also maintain a clean high quality cut as well. Two types of arbors are commonly found in slitting machines of current manufacture--the slip type and the packed type.
The knives of a slip arbor are carried on hubs that slide over the arbor and are secured with set screws in the desired positions. In order to minimize deflection, the arbor must have a relatively large diameter. The hubs contain set screws which when turned down force clamping pads against the surface of the arbor to secure the knives firmly on the arbor. To set the knives of a pair in the proper position, the location of the cut desired from the pair of knives is usually located by measuring with a tape measure from reference point on the machine. One of the knives is then moved over its arbor to the point located with the tape measure and the set screw of its hub is turned down to secure the knife. Once the knife is so positioned, an indicator gage should be brought against it while the arbor is turned slowly. With the indicator gage the knife is checked for wobble and usually adjustments must be made by loosening the set screws and tapping the knife lightly to eliminate the wobble. The same procedure is then repeated with the other knife of the pair, only its location is determined from the location of the previous knife, there usually being an axial gap on the order of 7 to 10 percent of the thickness of the metal sheet between the opposite cutting edges of the two knives.
On a packed arbor spacers separate the knives. These spacers are large enough and are machined with enough precision to eliminate the wobble inherent with conventional slip arbors, but present complexities in the selection of spacers and shims to properly locate the knives. Indeed, the entire arbor is usually removed from the machine and placed in a setup stand to install its complement of knives and spacers for any particular slitting job, and this in itself is a difficult procedure. Moreover, the selection of spacers and shims requires a considerable amount of skill. Furthermore, the spacers must be handled carefully, lest they may acquire knicks that will skew the knives and create a wobble as they rotate.
With both slip arbor and packed arbor machines the knives are usually handled apart from the arbor during loading and unloading, and if a knife is not needed for a particular slitting operation, it must be stored separately from the machine. This is somewhat inconvenient and increases the set up time.